David M. Richardson

Abstract Aim Reproductive traits are important mediators of establishment and spread of introduced species, both directly and through interactions with other life‐history traits and extrinsic factors. We identify features of the reproductive biology of Australian acacias associated with invasiveness. Location Global. Methods We reviewed the pollination biology, seed biology and alternative modes of reproduction of Australian acacias using primary literature, online searches and unpublished data. We used comparative analyses incorporating an Acacia phylogeny to test for associations between invasiveness and eight reproductive traits in a group of introduced and invasive (23) and non‐invasive (129) species. We also explore the distribution of groups of trait ‘syndromes’ between invasive and non‐invasive species. Results Reproductive trait data were only available for 126 of 152 introduced species in our data set, representing 23/23 invasive and 103/129 non‐invasive species. These data suggest that invasives reach reproductive maturity earlier (10/13 within 2 years vs. 7/26 for non‐invasives) and are more commonly able to resprout (11/21 vs. 13/54), although only time to reproductive maturity was significant when phylogenetic relationships were controlled for. Our qualitative survey of the literature suggests that invasive species in general tend to have generalist pollination systems, prolific seed production, efficient seed dispersal and the accumulation of large and persistent seed banks that often have fire‐, heat‐ or disturbance‐triggered germination cues. Conclusions Invasive species respond quicker to disturbance than non‐invasive taxa. Traits found to be significant in our study require more in‐depth analysis involving data for a broader array of species given how little is known of the reproductive biology of so many taxa in this species‐rich genus. Sets of reproductive traits characteristic of invasive species and a general ability to reproduce effectively in new locations are widespread in Australian acacias. Unless there is substantial evidence to the contrary, care should be taken with all introductions.

Expansion and decline of species are natural phenomena (Levin, 2000). However, owing to the increasing infl uence of humans worldwide, the processes driving expansion and decline have speeded up dramatically. Hence, we have the current biodiversity crisis. Humanmediated forces are making some species rarer (ie, driving them towards extinction) while at the same time making some species expand their ranges (‘invasive’ sensu Richardson et al., 2000). Undisputedly, the immediate causes for extinction of native species and invasiveness of aliens are extrinsic factors, such as habitat destruction and climate change. However, the ultimate causes have to be ecological and life-history characteristics of species (Kotiaho et al., 2005). Therefore, important research directions in conservation biology and invasion biology are the analyses of species traits associated with rarity (Murray et al., 2002) and invasiveness (Pyšek and Richardson, 2007), respectively. The first are important for prioritizing conservation efforts, and the second are important for prioritizing eradication efforts and the development of screening protocols of potential invasiveness of species considered for introduction to other regions. Unravelling the links between species traits and extrinsic factors is highly complex, particularly because assessment of the causes of rarity and invasiveness relies mainly on retrospective analyses since large-scale controlled experiments are often not feasible (Richardson et al., 2004). However, with the increasing availability of large, widely accessible databases and analytical approaches (eg, Wilson et al., 2007), it is becoming easier to test which traits are associated with rarity and invasiveness, and under which conditions.